Lyme Disease Ecology Simulation Student Task

Anchoring Phenomenon: In New England forests, the number of human Lyme disease cases fluctuates wildly from year to year. Oddly, these spikes do not seem to happen at random, nor do they happen immediately when there are lots of deer.

In this task, you will use an interactive simulation of a forest ecosystem to evaluate claims about how interactions between oak trees, white-footed mice, deer, and ticks maintain stability or result in change, driving the risk of Lyme disease.

Teacher Notes & Alignment

• NGSS Standard: HS-LS2-6: Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem.
• Science and Engineering Practice (SEP): Engaging in Argument from Evidence. Students will evaluate claims and reasoning regarding ecosystem stability and responses to disturbance.
• Disciplinary Core Idea (DCI): LS2.C: Ecosystem Dynamics, Functioning, and Resilience. Students explore how the interconnected populations of trees, mice, and ticks respond to modest disturbances (masting) and extreme fluctuations (deer population changes).
• Crosscutting Concept (CCC): Stability and Change. Students use the simulation to model how the ecosystem changes and whether it returns to a stable state.
• Evidence Statements Addressed:
  • 1a: Identify the given explanation supported by claims, evidence, and reasoning regarding complex interactions maintaining consistent numbers in stable conditions.
  • 2a (ii, iii): Identify and describe additional evidence regarding the relationships between species and changes in numbers subject to modest/extreme change.
  • 3c (i, ii): Assess the logic of the reasoning regarding how modest disturbances result in maintenance of consistent numbers, while extreme fluctuations challenge ecosystem functioning.
• Estimated Time: 45 - 60 minutes
• Materials: Computer or tablet with internet access, “Lyme Disease Ecology” simulation.

Phase 1: Engage

Claim 1 to Evaluate: “The risk of a human getting Lyme disease this summer depends primarily on how many deer are in the forest right now.”

1. Based on your current knowledge of ecosystems and food webs, do you think this claim is entirely accurate, partially accurate, or inaccurate? _____

2. What additional organisms (besides deer and humans) might be part of the Lyme disease ecosystem? _____

Phase 2: Explore

Open the Lyme Disease Ecology Simulation.

Part A: Baseline Stability

Click “Next Year” 5 times without changing any settings.

1. Observe the Population Chart and the numerical stats.
2. Record the baseline values:
   • Mouse Population multiplier: _____
   • Infected Nymphs (numeric index) OR Risk Level (categorical): _____
3. Does the ecosystem naturally remain stable if no major disturbances occur? _____

Part B: The Modest Disturbance (Acorn Mast Year)

Oak trees occasionally produce massive amounts of acorns in a single year, known as a “mast year.”

1. Click the “Trigger Acorn Mast Year” button. The “Oak Tree Acorn Production” stat will show “Pending Mast…”.
2. Click “Next Year” and observe what happens in “Year 1” (the mast year).
3. Click “Next Year” again (Year 2) and observe the Mouse Population.
4. Click “Next Year” again (Year 3) and observe the Tick Risk.

Data Collection Table 1: Effects of an Acorn Mast | Time | Event | Mouse Population Multiplier | Tick Risk Level | | :— | :— | :— | :— | | Year 0 | Baseline | | | | Year 1 | Acorn Mast | | | | Year 2 | 1 Year Post-Mast | | | | Year 3 | 2 Years Post-Mast | | | | Year 4 | 3 Years Post-Mast | | | | Year 5 | 4 Years Post-Mast | | |

Phase 3: Explain

Using the data from Table 1, address the following points:

1. Describe the cascade: Explain the relationship between the acorn mast, the mouse population, and the tick risk. Why is there a delay between the mast year and the spike in Lyme disease risk? _____

2. Evaluate Ecosystem Stability (Evidence Statement 3c.i): After the initial disturbance of the mast year, did the populations of mice and ticks continue to grow endlessly, or did the ecosystem eventually return to a stable state? Use evidence from your Year 4 and Year 5 data. _____

Phase 4: Elaborate / Evaluate

Now, let’s evaluate a more extreme disturbance and an engineered intervention.

Part C: Extreme Fluctuation (Deer Population)

1. Click Reset.
2. Change the Deer Population Factor (multiplier) slider from $1.0$x to $2.0$x.
3. Click “Next Year” 5 times.
4. How did doubling the deer population affect the baseline Tick Risk compared to Part A? _____

Part D: Intervention (Vaccinating Mice)

Scientists are developing vaccines that can be distributed in bait to wild mice, preventing ticks from contracting Lyme bacteria from them.

1. Click Reset.
2. Click “Vaccinate Mice”. (The button will turn green and say “Stop Vaccination”).
3. Trigger an Acorn Mast Year and click through 4 years.
4. Even though the mouse population boomed (as in Part B), what happened to the Tick Risk? _____

Final Deliverable (Evidence Statements 1a, 2a, 3c)

Re-evaluating Claim 1: Let’s look back at the original claim: “The risk of a human getting Lyme disease this summer depends primarily on how many deer are in the forest right now.”

Based on your evidence, write a paragraph to critique and revise this claim. In your revised explanation, you must:

• Identify how the complex interactions between acorns, mice, and ticks maintain relative stability, but cause predictable fluctuations.
• Explain why a modest disturbance (acorn mast) causes a delayed spike in risk.
• Argue whether focusing only on deer is sufficient to predict or control Lyme disease, citing your evidence from the simulation.

Extension Options

• Graphing: Have students export or recreate the simulation graph data in a spreadsheet to calculate the exact percentage increase in risk following a mast year.
• Policy Design: Ask students to design a public health advisory system for their local town based on the acorn crop size from the previous year.